It is a common practise to sort individual articles sequentially, for example according to their individual weight, colour, clarity etc. This is done for example in the case of diamonds and other stones, sweets, peas, tablets and other medical preparations, and many other articles. When the relevant quality has been measured or detected by appropriate sensing means, the articles must be correspondingly sorted. The sorting may comprise only two categories namely "pass" and "fail", but in many cases it is desirable to sort into a plurality of categories, for example ranges of weight or colour. For accurate sorting, the sorting means must be synchronized with the sensing means, and the articles must be presented to the sorting means with accurate placing and timing to avoid incorrect sorting. The articles may well leave the sensing means with some irregularity in speed, direction, position or timing, and such irregularities need to be reduced or eliminated before the articles are presented to the sorting means.
Ensuring that a sequence of articles is presented with accurately defined timing and placing is also desirable in other contexts, for example in presenting the articles to a sensing means for determining the weight, colour or some other quality.